Continuing from a previous topic about Headway LiFePO4 cells

[vhfman]

affordable-15-ah-battery

I've read about BMS's being less than reliable and consequently damaging cells. So with a BMS-less pack, say, 2X6s 10AH Headways, what would you need? How would you separate/connect the two packs for charging etc?
Need a LiFePO4-compatible RC Balance Charger that can cope with 6 cells plus Power Supply so you can charge to 3.6V each? How do you actually physically charge them? Photos would be good!
Then how do you ensure they don't get drained too low in use? A Volt &/or AH monitor obviously but is there some kind of simple pack LVC shut-off device or perhaps an alarm? (I think I've seen something on RC sites....)
If it came to replacing a cell would a new one cause problems in balancing even if charged to the same level as the others?

I know you will say it’s a lot easier to fit a BMS to the battery but I have had reliability problems in the past. May be it is possible, that some of the newer versions of BMS available now, mean that it could be worth a look again at a permanently attached BMS board. But in the meantime I use my tried and tested manual methods as described here.

As you probably know the Headway’s have a LiFePO4 cell chemistry, with a nominal cell voltage of 3.2V. For a 36v battery you need 12 cells in series to give a pack voltage of 38.4V. The charging voltage for a 12S battery is 43.8V. I have seen accounts that the cell voltage can be increased up to 4.0V with no apparent cell damage occurring. But that is not recommended by the manufacturers Headway. Personally I have found that taking the voltage much above 3.8v per cell is a waste of time, as the cells only accept a few more mA of charge above 3.65V. And I have noticed that cells that have been over voltage in the past seem to have a higher self discharge rate.

The type of charger used for LiFePO4 batteries should be a Constant Current/ Constant Voltage cc/cv.

Headway 38120S (10AH) cells have:-

• Internal Impedance of <6mΩ
• Maximum Charge Current 2C(20A)
• Maximum Continuous Discharge Current 3C(30A)
• Maximum Peak Pulse Discharge Current 10C(100A)
• Minimum Discharge Voltage 2.0V

For accessibility to individual cells I have made up the battery in 2 * 6S packs with balance leads and output leads attached to the cells. In use the 2 packs are connected in series 12S.

[url]http://farm5.staticflickr.com/4127/5396922866_565b4c4690_z.jpg[/URL]

With screw terminals instead of a welded or soldered tab connection, if a cell does go bad in the future, it is much easier to replace the bad cell. And as long as the new replacement cell is charged to the same state as the rest of the pack prior to putting the cell in the battery there should be no problems with balance.

Here are a couple of pictures showing my bulk charging setup using variable DC power supply with adjustable current limit (digimess SM5020).

[url]http://farm8.staticflickr.com/7206/7116571049_0f30f2fd75_z.jpg[/URL]

[url]http://farm8.staticflickr.com/7240/6970498638_f388d376ef_z.jpg[/URL]

There are a few videos on Youtube showing bulk charging some A123 cells with a similar power supply to mine.

[url=http://www.youtube.com/watch?v=o1TUAlvUliw&feature=related]Charging 12s2p A123 with Mastech Part 2 of 2 - YouTube[/URL]

I can charge the Headway as a 12S pack @ 43.8v up to 20A, but I generally charge at 10A or less which I think is kinder on the cells. I do have a 12S balancer which allows the batteries to be balanced as they are being charged @ up to 10A, or passively without the power supply. I can also use a cheap standard 5A 43.8V charger like this one from BMSBattery as the power source.

The other method of balance charging is to use one of the RC balance charges, with possible more accurate cell end point monitoring. I have a couple of iCharger 106B+, which are 6S 10A chargers along with 13.8v power supplies. You can parallel the two 6S packs of cells and balance charge as well. As these RC balance charges are powered from external power source, they can be used if you are away from a mains supply by using a 12v car battery. You must be careful not to flatten the car battery if you charge like this, as with over 250W load you can soon discharge the car battery.

[url]http://farm9.staticflickr.com/8161/6970504270_333b9cef44_z.jpg[/URL]

As regards LVC you can monitor at cell level using something like the celllog 8S M or the Chargery BM6 which can be set to give an audible alarm if an LV problem occurs. I don’t generally worry about LVC for the battery as the BLDC controllers have LV cut-off set around 31.5v for a 36v controller.

This is the celllog 8S which can record and store data a bit more expensive than the 8M.

[url]http://farm8.staticflickr.com/7072/7116578431_df4fa8cce5_z.jpg[/URL]


I have recently got one of the Speedict devices which are similar in use to the well known Cycle Analyst and can monitor and record all the parameters of the battery while in use, including Ah used, battery voltage etc, as well as speed and journey time. Which mean they act like a battery fuel gauge. But other simpler power meters are possible, like the Watts up or Turnigy Watt Meter and Power Analyzer.

Here is a picture comparison of 12S1P Headway 10Ah and 12S1P A123 2.3Ah packs.

http://farm8.staticflickr.com/7040/6970492944_736eb46219_z.jpg

Weight comparison of the batteries shown

• Headway 12S 4.34Kg
• A123 26650 12S 940g

Here is my homemade frame bag

http://farm8.staticflickr.com/7047/6970489780_d609020f2b_z.jpg

Chris

 

[jerrysimon]

Excellent post for others to follow if they wish. Thanks for taking the trouble to explain it all.

For bulk charging would it not just be possible to use a generic ebike lead acid (cc/cv) charger like I do for my A123 packs, but maybe one with a higher charging current. Mine is 1.6A so it would take 8-10 hrs lol.

Regards

Jerry

 

[muckymits]

Great..... saves asking more questions about mounting the cells. I still might manage to get mine back in the original battery case

Just one quick question, Ive just got a 8 port Turnigy and it was nowhere near the price of your Icharger with 6 ports, is it better quality or more functions, have I bought the wrong one

 

[vhfman]

Hi muckymits

I don’t know what cells your battery has, so not sure what charger you require. May be as you have gone for an 8S charger you have a ~48v 16S battery?

I presume that the charger you have is the Turnigy Accucel-8, which is 150W compared to the iCharger which is 250 W. And unless you need an 8S charger then there is no advantage there. The functionality will be pretty much the same for both chargers, so no problem with either charger. It’s just going to take longer to charge your battery packs with the Turnigy. As regards to price, I bought the iChargers a couple of years ago, and got a v good deal on them. I am certainly not recommending the iCharger over any other RC balance charger out there, although I do think the iCharger is well made. So no I don’t think you have bought the wrong charger; at least without further details of your battery.

I wonder what battery cells you are using? I hope you are able to get them into your case.

Thanks Jerry for your comments. As you may remember, I have ME, so writing coherent text is quite challenging. It took me most of yesterday to take some pictures, upload and write the text. And then I found loads of mistakes and had to edit the post (brain fug). I did have to sleep in the afternoon. And it’s just over a week since I slipped and badly bruise my bum. I am still finding it difficult to get comfortable sitting or lying down! But fortunately as the weather has been so bad here, I wouldn’t have wanted to be riding my bike anyhow. I try to do a short walk each day, and it's been, and still is Umbrella time! There is certainly no shortage of water in my neighbourhood.

As regards using generic ebike chargers, as long as they output the correct voltage and are cc/cv, then yes. I have used the BMSBattery 240W one, and also one that came with the original battery I started with 4 years ago. That one is also low power @ 1.5A and takes over 6 hrs to charge a nearly flat battery.

Chris

 

[neptune]

Firstly, I would like to say a big thank you to both Jerrysimon and vhfman for the unselfish way you have shared your knowlege and experience on the forum. Solid Gold stuff. Chris, sorry to here about your fall, literally a pain in the ass. Bad as it was, you are lucky you did not bruise the coccyx, the bone at the bottom of the spine, and we all wish you a speedy recovery. Incidentally, with that "handle" are you a Radio Amateur?
A quick word on chargers. Somewhere on Endless Sphere, there is a very simple circuit to convert a basic charger to constant voltage/constant current. Just a couple of regulators and a handful of bits. I have always built my own chargers, by rewinding transformer to the required voltage . Transformers from microwave ovens are suitable, and it is not as daunting a task as you would think. I leave the 240 volt winding intact, and remove the 2000 volt coil, replacing it with a new winding to suit the purpose. Usually, the stampings are welded together , so I use a home made shuttle to do the winding. I always wind too many turns, and then remove a few at a time until I hit the right voltage .

 

[muckymits]

Thanks Chris, The charger was bought to charge a 7 cell LiPo from a Powercycle and more importantly to play around. So this battery might go in to wifes Izip and find something to fit the side mounts on my Izip. They are both at 24 volt so I know Ive got enough ports to play with.

And how many Hams are there on here? G0---

Btw that bum is going to be a funny colour for weeks, so no mooning, they can easily recognise you

 

[banbury frank]

Hi

WARNING Messing with Charging battery's with the wrong charger and NO BMS will result in Explosions off battery's And a Fire If you are going to Experiment charge the battery outside in a metal box

Frank

 

[jerrysimon]

Whilst some caution is advisable, LiFePO4 chemistry is inherently safe and these batteries will NOT explode. In fact I think Headway cells actually have built in venting ?

If this was the case then when a BMS failed the result would be similar. If anything, more caution would be advised when selecting charging methods to ensure you do not ruin expensive cells.

The A123 cells that I have can literally be cut in half or drilled through, without resulting in an explosion or a fire.

Regards

Jerry

 

[vhfman]

Ok muckymits on you details. I hope all works well for you.

No more mooning!

You are right about the amateur radio, but not G0. I took my RAE in 1969 and the GPO Morse test in 1972. My licence dates back to the early 1970’s as a G4. I am not active on the bands at the moment, but I was particularly active a few years ago on 2M, 70cm and 23cm, with lots of homebrew equipment especially antennas, power supplies and linear amps.

Frank, yes I agree with your warning about messing with batteries. But if you read my OP you will see that I am manual monitoring the battery status. And I agree with Jerry’s comments regarding Headway and A123 type batteries which are very stable in use. Not to be compared with RC Lipo batteries which also have no BMS, and are widely used around the world by hobbyists.

I will add that a built in BMS is no guarantee that the battery is safe when charging.

But I will say that working with any battery can be dangerous, especially most lithium chemistry batteries which have a very low internal resistance and can supply massive amounts of current if shorted or mishandled. This can result in Kentucky Fried Fingers, or worse as you say fire or explosion. This is true of course with any high capacity battery, including 12v lead acid car batteries.

Precautions when working with batteries are important like removing metal jewellery rings, chains and medallions which could accidentally cause a short. And making sure wires attached to the battery are insulated from accidentally short circuit.

Chris

 

[alban]

Aargh!... just lost my post - why does it time out and lose the lot!!!
Suffice to say for now thanks for this info and I appreciate as a fellow M.E.'er what it cost you. Will respond more later - when I've recovered!

 

[alban]

That's a comprehensive account Chris, thanks!
I'm intent on paralleling a Headway 10AH (as able to be fast-charged and discharged by itself at 25A no problem) with my stock Li-ion via Schottky. So this BMS-less option seems do-able as a novice. So I can balance charge the 2X6S Headways thro the same discharge leads then rely on the controller's LVC to protect the batt on discharge? I intend only re-charging the Headway batt when out & about so the Li-ion should be at LVC too. I'll use an alarm as to run out of juice is a big no-no for me - would just one 6 cell alarm be OK to use?
I like the idea I'm checking on the cells' health myself.
How robust are these chargers and PSUs? - I want to carry them on the bike in a backpack now and then. I'll prob try to adapt a 12v PC PSU 270W (recycling - and I'm a cheapskate!) or find an XBox 360 power brick as detailed by Scottyf's (I think) review in this link a610. That's the one I'm prob going to get.
Man, you're going to look like a baboon (from behind!) for a while!

 

[lessped]

affordable-15-ah-battery



I know you will say it’s a lot easier to fit a BMS to the battery but I have had reliability problems in the past. May be it is possible, that some of the newer versions of BMS available now, mean that it could be worth a look again at a permanently attached BMS board. But in the meantime I use my tried and tested manual methods as described here.

As you probably know the Headway’s have a LiFePO4 cell chemistry, with a nominal cell voltage of 3.2V. For a 36v battery you need 12 cells in series to give a pack voltage of 38.4V. The charging voltage for a 12S battery is 43.8V. I have seen accounts that the cell voltage can be increased up to 4.0V with no apparent cell damage occurring. But that is not recommended by the manufacturers Headway. Personally I have found that taking the voltage much above 3.8v per cell is a waste of time, as the cells only accept a few more mA of charge above 3.65V. And I have noticed that cells that have been over voltage in the past seem to have a higher self discharge rate.

The type of charger used for LiFePO4 batteries should be a Constant Current/ Constant Voltage cc/cv.

Headway 38120S (10AH) cells have:-

• Internal Impedance of <6mΩ
• Maximum Charge Current 2C(20A)
• Maximum Continuous Discharge Current 3C(30A)
• Maximum Peak Pulse Discharge Current 10C(100A)
• Minimum Discharge Voltage 2.0V

For accessibility to individual cells I have made up the battery in 2 * 6S packs with balance leads and output leads attached to the cells. In use the 2 packs are connected in series 12S.

[url]http://farm5.staticflickr.com/4127/5396922866_565b4c4690_z.jpg[/URL]

With screw terminals instead of a welded or soldered tab connection, if a cell does go bad in the future, it is much easier to replace the bad cell. And as long as the new replacement cell is charged to the same state as the rest of the pack prior to putting the cell in the battery there should be no problems with balance.

Here are a couple of pictures showing my bulk charging setup using variable DC power supply with adjustable current limit (digimess SM5020).

[url]http://farm8.staticflickr.com/7206/7116571049_0f30f2fd75_z.jpg[/URL]

[url]http://farm8.staticflickr.com/7240/6970498638_f388d376ef_z.jpg[/URL]

There are a few videos on Youtube showing bulk charging some A123 cells with a similar power supply to mine.

[url=http://www.youtube.com/watch?v=o1TUAlvUliw&feature=related]Charging 12s2p A123 with Mastech Part 2 of 2 - YouTube[/URL]

I can charge the Headway as a 12S pack @ 43.8v up to 20A, but I generally charge at 10A or less which I think is kinder on the cells. I do have a 12S balancer which allows the batteries to be balanced as they are being charged @ up to 10A, or passively without the power supply. I can also use a cheap standard 5A 43.8V charger like this one from BMSBattery as the power source.

The other method of balance charging is to use one of the RC balance charges, with possible more accurate cell end point monitoring. I have a couple of iCharger 106B+, which are 6S 10A chargers along with 13.8v power supplies. You can parallel the two 6S packs of cells and balance charge as well. As these RC balance charges are powered from external power source, they can be used if you are away from a mains supply by using a 12v car battery. You must be careful not to flatten the car battery if you charge like this, as with over 250W load you can soon discharge the car battery.

[url]http://farm9.staticflickr.com/8161/6970504270_333b9cef44_z.jpg[/URL]

As regards LVC you can monitor at cell level using something like the celllog 8S M or the Chargery BM6 which can be set to give an audible alarm if an LV problem occurs. I don’t generally worry about LVC for the battery as the BLDC controllers have LV cut-off set around 31.5v for a 36v controller.

This is the celllog 8S which can record and store data a bit more expensive than the 8M.

[url]http://farm8.staticflickr.com/7072/7116578431_df4fa8cce5_z.jpg[/URL]


I have recently got one of the Speedict devices which are similar in use to the well known Cycle Analyst and can monitor and record all the parameters of the battery while in use, including Ah used, battery voltage etc, as well as speed and journey time. Which mean they act like a battery fuel gauge. But other simpler power meters are possible, like the Watts up or Turnigy Watt Meter and Power Analyzer.

Here is a picture comparison of 12S1P Headway 10Ah and 12S1P A123 2.3Ah packs.

http://farm8.staticflickr.com/7040/6970492944_736eb46219_z.jpg

Weight comparison of the batteries shown

• Headway 12S 4.34Kg
• A123 26650 12S 940g

Here is my homemade frame bag

http://farm8.staticflickr.com/7047/6970489780_d609020f2b_z.jpg

Chris

what.? .!

 

[alban]

Hmmm... I wonder if you can respond to this guys. I asked GiantCod (RC stockist) about using the G.T. Power A6-10 200W Balancing Charger a610 to balance charge 2 packs of 6 LiFePO4 Headways (10AH) in parallel and I got this response which surprised me:

Hi,
In real terms what you are proposing is not advisable. Due to production spread/tolerances within individual cells you cannot balance charge in this way.

The charger is designed for model aircraft/boat/car battery packs with an absolute max dissipation as described. Perhaps there may be something a little more industrial available to charge your packs.

Regards,
Giantcod*

Any ideas as to whether they're just being over-cautious?
Thanks

 

[jerrysimon]

Alban why do you want to do them in parallel at the same time ?

With my A123s I have two 6s1p packs which I connect in series for my bike. Mostly I bulk charge them like this.

I check the balance occasionally using a cellog meter and if need be split the pack down into its two 6s1p packs and then charge balance them one at a time. I assume you can do the same with these Headway packs albeit more often given they do not hold balance as well ?

Regards

Jerry

 

[alban]

I wanted to parallel them as it was less hassle to plug in once and leave to charge fully - and Chris suggested above it was poss with his iCharger i.e. 'I have a couple of iCharger 106B+, which are 6S 10A chargers along with 13.8v power supplies. You can parallel the two 6S packs of cells and balance charge as well'.
Yes, so in parallel to balance them together when charging which is not poss in series? Didn't see the point in getting different chargers to do the job to bulk charge and then to balance.
I've read of people paralleling lipos with the same capacity with my intended charger (linked to above) e.g. 'Anyway I charge 4x 6s 22.2v 5000mah lipo batteries at 9amp. This is the max the charger can kick out as well as pushing my psu. However although it gets warm internal operating temp at 70c it charges all 4 in parallel in 2 and a half hours all fully balanced. Which is pretty good and I use these batteries for an ebike.' hence I was a bit surprised at GiantCod's response to to my enquiry about charging the same capacity Headways....

So my Q is - will a balance charger that is like the iCharger 106b balance charge my 2X 6s1P Headway 10Ah packs in parallel OK and at a good rate (like at least 4A as it's a 200W/10A charger) despite what GiantCod say (who will not have come across this sort of use)? Thanks.